I have an upper left molar which required an emergency root canal during a hiking trip in France due to an
abscess in 2011. They redid the root canal (or finished it anyhow) when I returned home, but were not entirely happy with how it was done.
Since then, I've had fleeting pain around the tooth, but repeated xrays showed nothing at all unusual.
In October 2013 I was in Hong Kong for a job interview and the gum above the tooth became sore and bruised.